The present invention relates to a device for improved feeding of secondary combustion air into the area of flue gas channels of horizontal coke oven chambers. Secondary combustion air is supplied into the flue gas channels from secondary air ducts which are usually installed under the flue gas channels. The present invention also relates to a device for controlling the feed volume of secondary air from the secondary air ducts into the area of flue gas channels. Owing to the improved supply and control of secondary air into the flue gas channels, the control of heat distribution and the combustion of coking gases in “Heat-Recovery” or “Non-Recovery” coke oven chambers can be improved.
In most cases, coke oven chambers of the “Heat-Recovery” or “Non-Recovery” type are set-up in such a manner that coal carbonization is realized in a horizontally charged coke oven chamber which is sealed to air. During the carbonization of coal, coal by-products evolve which are captured in conventional horizontal coke ovens and passed on for further processing. Coal by-products are mainly composed of gases, carbon monoxide, carbon dioxide, and higher-grade hydrocarbons. To ensure adequate supply of carbonization heat, conventional coke ovens must be heated by combustion of externally supplied combustion gases. In “Non-Recovery” or “Heat-Recovery” type coke ovens, the coal by-products derived from the carbonization process are utilized as combustion gases to generate the combustion heat needed for coal carbonization. To achieve the most even possible heating-up of the coke cake from all sides, only part of the coking gases is burnt above the coke cake, and partly burnt coking gases are burnt completely only underneath the coke cake in what are called flue gas channels.
In technical terms, this is realized by directly heating the upper side of the coke cake in the oven space by heat transfer procedures resulting from combustion processes with supply of an sub-stoichiometric amount of air. Coal by-products thus developing during coal carbonization are discharged as coking gases into an oven free space located above the coke cake which is left non-charged when charging the coke oven chamber with coal. Located in the ceiling of the coke oven or in its lateral walls are openings through which a certain amount of air, i.e. the so-called primary air, can be supplied into the upper section of the coke oven. A partial amount of the coking gases is burnt with primary air so that these gases heat the coke cake sufficiently from above to ensure adequate coal carbonization. The openings for introduction of primary air may be both controlled and non-controlled. An example for a controlled supply of primary air is given in WO 2006128612 A1.
Partly burnt coking gases from coal carbonization are conducted through so-called “downcomer” channels which may be accommodated in coke oven chamber walls, coke oven chamber doors or even in the coke cake into the flue gas channels located underneath the coke oven chamber and also designated as sole heating flues. There, they are completely burnt with another amount of air, which is called secondary air. By combustion of the residual carbonization products, the coke cake is also heated from below, because a substantial amount of heat is created by this downstream combustion with secondary air in the flue gas channels. The bottom between flue gas channels and coke oven chamber is relatively thin to ensure good heat transfer from flue gas channels into the coke oven chamber. To optimally exploit the heat from secondary combustion, the flue gas channels frequently extend like a meander under the coke oven chamber floor. The flue gas channels may be available in simple form, but also in multiple form. The flue gas channels are closed at all sides towards the atmospheric environment. Flue gas is conducted via an additional channel into a flue gas stack.
Secondary air for combustion is conducted from below into the flue gas channels. Located underneath the flue gas channels is a secondary air duct comprised of an opening to the environment and serving for pre-warming of cool ambient air on the one hand and distributing supplied secondary air over the flue gas channel(s) on the other hand. Secondary air can be supplied in a controlled manner into the secondary air duct. Accordingly, flaps or valves may be provided at the air intake opening for secondary air at the external openings of the secondary air ducts. These control devices make it possible to adequately control the stoichiometry of supplied air. Though these flaps or valves would be sufficient for controlling the secondary air, cold air is conducted through these feeder devices into the secondary air ducts and, thereby, into the flue gas channel. Moreover, the required secondary air cannot be conducted to all points in the flue gas channel, but is distributed in a non-controlled manner after having passed through the flap to all points of the flue gas channel located under the coke oven chamber.
Therefore, there are configurations feeding air in a controlled manner through the “downcomer” channels into the coking gas. U.S. Pat. No. 6,187,148 B1 describes a horizontal chamber-type coke oven which can conduct air through an opening in laterally installed “downcomer channels” into the “downcomer” channels. Since the opening has a controlling device, the thermal gradient n the coke oven as well as the gas pressure in the interior of the coke oven chamber can be controlled. But it is not possible to selectively influence the temperature distribution and the thermal gradient in the interior of the flue gas channels under the coke oven chamber floor so as to generate based upon a controlled secondary combustion an even planar heating under the coke bed to be heated-up. And it is not possible either to control the stoichiometry of combustion in flue gas channels.
WO 2006103043 A1 describes a coke oven design according to which secondary air is conducted from secondary air ducts through connecting channels into the flue gas channel. These are so installed that secondary air is distributed via precisely selected positions in the flue gas channel. In this manner, secondary air is fed over the entire length of the flue gas channel rather than at one position of the flue gas channel. In principle, this can be realized at arbitrary positions spread over the flue gas channel which extends in form of a meander. These vertical connecting channels from the secondary air ducts to the flue gas channels are so configured that combustion can be realized.
The flaps in the external openings of the secondary air ducts can regulate the air admission in such a manner that the air volume of supplied secondary air is controllable. But it is not possible to distribute the volume of supplied secondary air punctually. And it is not possible either to control the volume of supplied secondary air at a distinct position of the flue gas channel. According to prior art in technology, a control of secondary air volume is only feasible via flaps at the external openings of secondary air ducts. By this approach, however, secondary air is fed in a non-controlled manner over the entire length of the flue gas channel. Consequently, some positions in the flue gas channel experience an excessive supply of secondary combustion air, while other positions remain short in supply. As a result, those positions with a supplied excessive volume of secondary combustion air experience a cooling-off or overheating, while those positions with an insufficient supply of combustion air experience incomplete combustion.